A Multi-User Multi-Input Multi-Output (MU-MIMO) system can achieve a full multiplexing gain and a significant throughput improvement by means of linear beamforming precoding at a transmitter. The accuracy of channel information acquisition has a significant influence on the gain of the MU-MIMO system in Frequency Division Duplex (FDD) configuration.
For the MU-MIMO system, codebook feedback is a technology to realize channel information acquisition and user scheduling. However codebook design adaptability and its granularity have become great challenges and bottlenecks in the MU-MIMO application in the FDD system. For example, a current Re1.10 4Tx codebook is not suitable for 4Tx cross-polarized antenna configuration, which restricts an efficient application of MU-MIMO.